printk: ringbuffer: fix errors in comments

printk: ringbuffer: fix errors in comments

The printk ringbuffer implementation is described in the comment as
using three ringbuffers, but the current implementation uses two (desc
and data). Update the comment so it matches the code.

Fix few more known issues in the comments.

Signed-off-by: Loïc Grégoire <loicgre@gmail.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20260328021855.53956-1-loicgre@gmail.com
[pmladek@suse.com: Fixed few more issues in the comments by John Ogness.]
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>